The status byte summary register is cleared when:
• You execute a *CLS (clear status) command.
• Querying the standard event and questionable data registers will clear
only the respective bits in the summary register.
The status byte enable register (request service) is cleared when:
• You turn on the power and you have previously configured the meter
using the *PSC 1 command.
• You execute a *SRE 0 command.
The status byte enable register will not be cleared at power-on if you
have previously configured the meter using *PSC 0.
Using Service Request (SRQ) and Serial POLL
You must configure your bus controller to respond to the IEEE-488 service
request (
SRQ) interrupt to use this capability. Use the status byte enable
register (
SRE) to select which summary bits will set the low-level
IEEE-488 SRQ signal. When the status byte “request service” bit (bit 6) is
set, an
IEEE-488 SRQ interrupt message is automatically sent to the bus
controller. The bus controller may then poll the instruments on the bus to
identify which one requested service (the one with bit 6 set in its status
byte). The request service bit is only cleared by reading the status byte
using an
IEEE-488 serial poll or by reading the event register whose
summary bit is causing the service request.
To read the status byte summary register, send the
IEEE-488 serial poll
message. Querying the summary register will return a decimal value
which corresponds to the binary-weighted sum of the bits set in the
register. Serial poll will automatically clear the “request service” bit in
the status byte summary register. No other bits are affected. Performing
a serial poll will not affect instrument throughput.
Caution
The IEEE-488.2 standard does not ensure synchronization between your
bus controller program and the instrument. Use the *OPC? command to
guarantee that commands previously sent to the instrument have
completed. Executing a serial poll before a *RST, *CLS, or other
commands have completed can cause previous conditions to be reported.
Chapter 4 Remote Interface Reference
The SCPI Status Model
162
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